1. Field of the Invention
The present invention relates to a shock absorber that creates a damping force for restraining vibratory motions of an object that is elastically supported by a supporting member, for example, a vehicle body. More particularly, the invention relates to a variable-damping force shock absorber in which the damping force can be changed.
2. Description of the Related Art
A conventional shock absorber apparatus is formed by various components as follows. A cylinder containing operating fluid is divided into first and second chambers by a piston disposed in the cylinder slidably in directions of an axis thereof. A hollow piston rod is connected at an end portion thereof to the piston. Another end portion of the hollow piston rod protrudes from an end face of the cylinder. A spool of a valve mechanism is provided at a piston-side end portion of the piston rod in such a manner that the spool is displaceable in directions of an piston rod axis. In accordance with the displacement of the spool in a direction of the piston rod axis, the valve mechanism changes the opening of a communication passage interconnecting the first and second chambers. An actuator is substantially made up of a stator mounted to an inner peripheral surface of the piston rod, a rotor disposed facing the stator so as to rotate about the piston rod axis relative to the stator, and a rotating body supported on an inner peripheral surface of the piston rod for rotation about the piston rod axis. The rotating body is fixed to the rotor so that the rotating body rotates together with the rotor. The actuator outputs rotating drive force created by rotation of the rotor via the rotating body. The shock absorber apparatus further includes a drive force converting mechanism that converts rotating drive force from the actuator into drive force in a direction of the piston rod axis. Furthermore, the drive force converting mechanism transfers the converted drive force to the spool of the valve mechanism so as to displace the spool in a direction of the piston rod axis. In the conventional shock absorber apparatus, the rotor of the actuator and the drive force converting mechanism are disposed overlapping each other in a direction of a radius of the piston rod, as disclosed in, for example, Japanese Patent Application Laid-Open No. HEI 5-60165.
However, since the rotor of the actuator and the drive force converting mechanism are disposed overlapping each other in a radial direction with respect to the piston rod, this conventional shock absorber apparatus has a problem of an increased diameter of the piston rod.